Fiber size and number in workers exposed to processed chrysotile asbestos, chrysotile miners, and the general population

Our plain-English summary of Fiber size and number in workers exposed to processed chrysotile asbestos, chrysotile miners, and the general population, by A. Churg, B. Wiggs (American Journal of Industrial Medicine, 1986).

The study

• Authors: A. Churg, B. Wiggs
• Journal: American Journal of Industrial Medicine
• Published: 1986;9(2):143-52
• Cited by: 69 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000384).

Abstract

We analyzed chrysotile and chrysotile-associated amphibole (largely tremolite) asbestos fibers in 21 workers exposed to various types of processed (milled) chrysotile ore, 20 long-term chrysotile miners, and 20 members of the general population (controls). Significantly greater amounts of both chrysotile and tremolite were found in processed-ore workers and miners than in controls. On average, the mean fiber lengths and aspect ratios for the mining and processed-ore-exposed workers were similar and were significantly greater than the values seen in the controls; within the processed-ore group, there was a marked variation in these parameters, and some workers appeared to be exposed to fairly long, thin fibers. It was found empirically that the fiber size data, and to a lesser extent the concentration data, could be used to classify workers accurately into those with processed-ore exposure and controls. We conclude that fiber sizes in the lungs of processed-ore-exposed workers are similar to those of chrysotile miners and are considerably longer than those found in the general population; some processed-ore workers have longer fibers which might be responsible for higher disease incidences in certain working groups; tremolite accompanies chrysotile in a variable proportion of workers exposed to processed chrysotile products and might be important in the genesis of mesothelioma in such workers; and mineralogic analysis will usually detect exposure even when chrysotile has largely disappeared from lung tissue.

In plain English

This study measured asbestos fibers in lung tissue taken at autopsy from three groups. The first was 21 workers exposed to processed (milled) chrysotile ore, such as shipyard, insulation, brake and textile workers. The second was 20 long-term Quebec chrysotile miners. The third was 20 Vancouver men over 50 with no occupational dust exposure, who served as controls. Using electron microscopy, the authors counted and measured chrysotile and the amphiboles that come with it, about 95% of which were tremolite. Processed-ore workers had significantly higher chrysotile and tremolite concentrations than controls, though values overlapped widely. Miners had markedly higher concentrations. Amosite and crocidolite were found in 17 of 20 processed-ore cases analyzed. Fibers were significantly longer in both exposed groups than in controls, and fiber sizes varied widely among processed-ore workers. A formula based mainly on chrysotile fiber size correctly classified 15 of 21 processed-ore workers and 18 of 20 controls. The authors concluded that mineral analysis will detect most occupational chrysotile exposure and that tremolite might matter for mesothelioma. They noted that actual exposure levels were unknown.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Comparison of asbestos fiber types, concentrations and sizes in autopsy lung tissue from three groups, analyzed by electron microscopy
• Who was studied: 21 referred autopsy cases with exposure to processed chrysotile ore (8 shipyard workers, 6 insulators, 3 brake workers, 2 textile workers, 2 manufacturing workers); 20 long-term workers in the Quebec chrysotile mining and milling industry; 20 male Vancouver residents over age 50 with no history of occupational dust exposure (controls)
• Exposure: Processed (milled) chrysotile ore, usually accompanied by commercial amphibole (amosite and crocidolite), in various industries; chrysotile mining and milling; general-population background exposure. Fibers studied were chrysotile and chrysotile-associated amphiboles (about 95% tremolite, most of the rest actinolite).
• Main results:
  • Mean chrysotile and tremolite concentrations in the processed-ore group were significantly greater than in controls (each p less than 0.02), but values overlapped widely between processed-ore workers and controls
  • Mean chrysotile concentrations (millions of fibers per gram dry lung): controls 0.3, processed-ore workers 11, miners 94
  • The chrysotile miners had markedly higher concentrations of both chrysotile and tremolite
  • Commercial amphiboles (amosite and crocidolite) were found in 17 of 20 processed-ore cases analyzed (one case not analyzed), at a mean of 10 million fibers per gram dry lung, compared with 0.01 million in controls
  • Tremolite concentrations equaled or exceeded chrysotile concentrations in 13 of 20 controls, 11 of 21 processed-ore workers and 18 of 20 miners
  • Tremolite was found in every occupational subgroup of the processed-ore workers
  • Mean chrysotile fiber lengths were significantly longer in processed-ore workers and in miners than in controls (p less than 0.001 for each)
  • Mean tremolite fiber size was greater in the processed-ore group than in miners (p less than 0.02); mean chrysotile size did not differ between these two groups
  • Aspect ratios for chrysotile and tremolite were significantly greater in both exposed groups than in controls (each p less than 0.001), and were the same in miners and processed-ore workers
  • Within the processed-ore group, shipyard workers had the lowest fiber concentrations on average and the shortest fibers
  • A discriminant formula using fiber concentrations and sizes correctly classified 15 of 21 processed-ore workers and 18 of 20 controls; chrysotile fiber size was the most important feature in the separation
• The authors' conclusion: The authors concluded that fiber sizes in processed-ore workers' lungs are similar to miners' and longer than the general population's. They also concluded that some processed-ore workers have longer fibers that might be responsible for higher disease rates in certain groups, and that tremolite accompanies chrysotile in a variable proportion of these workers and might be important in causing mesothelioma. Finally, they concluded that mineralogic analysis will detect most cases of occupational chrysotile exposure.
• Limitations the authors state:
  • The study looked retrospectively at a few selected workers with no details of actual exposure levels
  • Broad conclusions cannot be drawn from the small number of brake workers (and other small subgroups)
  • The classification criteria do not always work: they mistakenly identify apparently unexposed cases and miss cases that probably had exposure
  • Each laboratory would have to generate its own data and formulas, and the criteria apply strictly only to the reference population used
  • Finding a fiber of a given length depends on how many fibers are counted, so it may be less reliable than using a mean fiber size

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile, Tremolite.

Medical terms in this study, explained in our Lexicon: Chrysotile, Amphibole Group, Tremolite, Fiber Length, Aspect Ratio (Length-to-diameter ratio), Mesothelioma.

Related studies

• Mineralogic correlates of fibrosis in chrysotile miners and millers — A. Churg, J.L. Wright, et al. (1989)
• Fiber burden and patterns of asbestos-related disease in chrysotile miners and millers — A. Churg, J.L. Wright, et al. (1993)
• Respiratory cancer in chrysotile textile and mining industries: exposure inferences from lung analysis — P. Sebastien, J.C. McDonald, et al. (1989)
• Lung mineral fibers of former miners and millers from Thetford-Mines and asbestos regions: a comparative study of fiber concentration and dimension — A. Nayebzadeh, A. Dufresne, et al. (2001)
• The morbidity and mortality of vermiculite miners and millers exposed to tremolite-actinolite: Part I. Exposure estimates — H.E. Amandus, R. Wheeler, et al. (1987)
• Environmental pleural plaques in residents of a Quebec chrysotile mining town — A. Churg, L. DePaoli (1988)

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